Making voting public would go a long way
...towards LOTS of drama, enemy lists, political intrigue, etc.
Stack Overflow makes cast vote counts public, so one could get an idea of who is doing the voting. Figuring out who is voting on what would only be possible if you're watching everyone always (and even then it won't work if user displays only update periodically).
I do think that there's value in someone looking at the vote graph, be it humans or automated processes.
I've gotten sufficient evidence from support that voiceofra has been doing retributive downvoting. I've banned them without prior notice because I'm not giving them more chances to downvote.
I'm thinking of something like not letting anyone give more than 5 downvotes/week for content which is more than a month old. The numbers and the time period are tentative-- this isn't my ideal rule. This is probably technically possible. However, my impression is that highly specific rules like that are an invitation to gaming the rules.
I would rather just make spiteful down-voting impossible (or maybe make it expensive) rather than trying to find out who's doing it. Admittedly, putting up barriers to downvoting for past comments doesn't solve the problem of people who down-vote everything, but at least people who downvote current material are easier to notice.
Any thoughts about technical solutions to excessive down-voting of past material?